ObjectiveRare earth elements(REE) are one of the most important tracers in soil erosion study. Understanding the content variation of REEs alongside particle size ranges is significant to accurately quantify soil erosion rates.MethodBased on the REE contents in different particle size ranges(< 1, 1-10, 10-50, 50-250 and 250-1000 μm) of soil/sediment samples measured by Samonova et al.(2020), this study analyzed the effects of valley morphology, landforms, erosional and depositional areas on the contents and enrichment coefficient of REE in soil/sediment at the left bank of the Protva River in Russia. Landform types including hillslope, gully slope/wall, valley bottom and alluvial fan, were separately selected from a "U" and a "V" shape valley, respectively. These four landforms were further classified into erosional (i.e., hillslope and gully slope/wall) and depositional areas (i.e., valley bottom and alluvial fan).ResultThe results showed that: (1) The contents of light rare earth elements (LREE), heavy rare earth elements (HREE) and total rare earth elements (ΣREE) were all decreased with the increase of particle size ranges under the four landform types of "U" and "V" shape valleys. Under the condition of the same landform types, the contents of LREE, HREE and ΣREE in fine particles (< 50 μm) of the "U" shaped valley were 14.6%-24.7%, 10.0%-33.5% and 14.2%-21.1% lower than those of the "V" shaped valley, respectively. (2) Both LREE and HREE were enriched in fine particles at all landform types for both "U" and "V" shape valleys. Particularly for the "V" shape valley, LREE and HREE were significantly enriched in < 10 μm particles. (3) Comparing the erosional and depositional areas, the enrichment degree of LREE and HREE in the fine particles of the depositional areas in both "U" and "V" shape valleys was significantly (P < 0.05) higher than that of the erosional area.ConclusionAccordingly, REE were enriched in fine particles regardless of river valley shapes, landforms, and erosional or depositional areas. However, both valley shape and erosion-deposition processes had important impacts on the REE content variation in different particle size ranges.